Various types of liquid waste accumulated at reprocessing facilities after treatment of spent nuclear fuel discharged from nuclear power stations contain many radioactive nuclides including long-lived .beta. and .gamma. nuclides of cesium and the like and transuranium elements such as uranium, plutonium and the like. For the treatment of radioactive liquid waste, it is necessary to reduce the amount of radiation by separating and removing radioactive nuclides from the liquid waste in order to reduce radiation exposure.
In general, radioactive liquid waste is treated by means of evaporation concentration, coagulating sedimentation, ion exchanging and the like.
In the evaporation concentration process, liquid waste to be treated is put in an evaporator and heated under atmospheric or reduced pressure to allow only moisture to evaporate, thereby concentrating the radioactive liquid waste to a reduced volume. The evaporated moisture is recovered using a condenser. On the other hand, the thus concentrated liquid waste is subjected to further treatment such as bituminization or the like depending on the radioactive nuclides present in the waste.
The evaporation concentration process, however, has disadvantages in that because corrosion-resistant materials are required, the decontamination factor (DF) decreases due to evaporation of radioactive nuclides which also occurs and the volume-reducing effect is not sufficient.
In the coagulating sedimentation process, radioactive nuclides in the liquid waste are removed after their coagulation and precipitation. Radioactive nuclide-including sludge in which the radioactive nuclides are incorporated is subjected to dehydration treatment, and the resulting residue is treated as solid waste, and the supernatant fluid is treated as low-level liquid waste.
In the coagulating sedimentation process, however, the sludge formed has a high moisture content which causes a difficulty in carrying out the dehydration treatment, thus entailing a disadvantage in that the volume-reducing effect is not sufficient.
In the ion exchanging process, ions of interest are removed from the liquid waste by conducting ion exchange using an ion exchange resin. The spent resin containing the ions of interest is treated as solid waste, and the liquid portion after the treatment is treated as low-level liquid waste.
A chelate resin may be used instead of an ion exchange resin in a process similar to the ion exchange process.
However, when an ion exchange or chelate resin which is commonly used for the removal of metals from general liquid waste is applied to the treatment of radioactive liquid waste, it is difficult to use such a resin because of the tendency toward deterioration of such an organic polymer resin due to the action of radiation. Even where such an application could be effected, a problem of selectivity occurs. For example, virtually nothing is known about an adsorbent useful for the selective separation and removal of transuranium elements such as plutonium and the like which are present in a small amount in liquid waste of high uranium content.
Inorganic adsorbents may have radioactive resistance, but nothing is known on an inorganic adsorbent which has excellent adsorptivity. On the other hand, an adsorbent in which a ferrocyanate as an inorganic functional group is supported on an acrylic fiber as an organic support is disclosed in JP-B-63-24415 (the term "P-B" as used herein means an "examined Japanese patent publication"). This adsorbent, however, has disadvantages in that the functional group is not selective for the adsorption of transuranium elements and the support, being organic, has poor durability.
Also, JP-B-60-51491 discloses a phenol-based chelate resin which has an aminomethylphosphonic acid-type functional group, and which is described as having excellent uranium-adsorbing ability. This resin, however, is not capable of selectively adsorbing plutonium present in radioactive liquid waste.
In addition to the above described disadvantages, the ion exchanging and chelate resin processes have other problems in that each of these processes generates a large quantity of secondary wastes such as incombustible or flame retardant spent resin, liquid waste after resin washing and the like, and insufficient volume-reducing effect arises.
Although the volume of spent organic ion exchange resin may be reduced by incineration, generation of harmful gas, formation of smoke dust and scattering of radioactive nuclides all occur. In addition to such problems, the resin cannot be incinerated completely, leaving a soft charcoal residue which causes another problem by scattering atomized dust containing radioactive nuclides when the residue is treated. As a result, incineration of this type of resin is practically impossible.
Thus, as has been described above, the prior art adsorbents have common problems in that they have poor durability against radiation and transuranium elements in radioactive liquid waste are not adsorbed selectively. In addition, the prior art volume-reduction treatment methods have problems in that secondary wastes are generated in a large quantity, insufficient volume-reducing effect arises and the facility cost becomes high because of the necessity to use corrosion-resistant materials.